1. Field of the Invention
The present invention relates to a field emission cathode device made of a semiconductor substrate.
2. Description of the Related Art
The field emission cathode device is a source of electrons and comprises a cathode electrode layer, an emitter tip (or emitter tips) having a conical shape and formed on the cathode electrode layer, and a gate electrode layer arranged above the cathode electrode layer with an insulating layer arranged between the cathode electrode layer and the gate electrode layer. The insulating layer and the gate electrode layer have respective, aligned apertures in which each corresponding emitter tip is arranged. The distal end of the emitter tip is at the level of the inner wall of the aperture in the gate electrode. A field is created near the distal end of the emitter tip to induce emission of electrons therefrom when a voltage is applied between the cathode electrode layer and the gate electrode layer.
The field emission cathode device can be fabricated, in a very small size, by processes such as etching or vapor deposition used for fabricating semiconductor devices, and can be used, for example, in a micron-size vacuum tube (micro-vacuum-tube). Electrons in the field emission cathode device have a higher mobility than those in a semiconductor device, and the field emission cathode device offers high-speed operation at a high temperature and is resistant to damage by radiation. With these characteristics, the field emission cathode device can be expected to be used in a variety of applications, such as a microwave element, a super-high-speed arithmetic element, in radioactive or high-temperature environments, or as a display device.
The display device includes a plurality of emitter tips, used as electron guns, for constituting a plurality of pixels or light emitting elements (LEEs). For example, the article entitled "Recent Development on Microtip Displays at Leti" in the Technical Digest of IVMC '91 discloses a flat display device comprising a field emission cathode device including a plurality of micro electron guns and a phosphor display as an anode. The field emission cathode device comprises a glass substrate, a cathode electrode layer formed on the glass substrate, and a gate electrode layer arranged above the cathode electrode layer via an insulating layer. The cathode electrode layer includes a plurality of elongated strip-like cathode electrodes (cathode lines) extending in parallel to each other, and the gate electrode layer includes a plurality of elongated strip-like gate electrodes (gate lines) extending in parallel to each other and perpendicular to the cathode electrodes for and constituting a matrix with the cathode electrodes. The intersections of the cathode and gate electrodes constitute corresponding LEE regions. A plurality of emitter tips is provided on each of the LEE regions.
Since a glass substrate is used in this prior art, it is possible to form the cathode electrodes directly on the glass substrate without any insulation between two adjacent cathode electrodes. It is, however, desired that the substrate and the cathode electrodes be made of a semiconductor material so as to best utilize semiconductor fabricating processes. However, it is not possible to form a cathode electrode layer, comprising a plurality of cathode electrodes, directly on the semiconductor substrate since the semiconductor is conductive.